Water-resistant indurated fiber and method of making the same



Patented Nov. 3,193 6 UNITED STATES v 2,059,947 PATENT OFFICE" WATER-RESISTAN T INDURATED FIBER AND METHOD OF MAKING THE SAME Duncalf W. Hollingworth, Newark, Del., assignor to Continental-Diamond Fibre Company, Newark, Del., a corporation of Delaware No Drawing.

Application October 30, 1933, Serial No. 695,949

30 Claims. (01. 154 2) The present invention relates to'a water-resistant indurated fiber and to the method of making the same, and more particularly it relates to an improved indurated fiber which possesses very low water-absorptive qualities and'at the same time is characterized by the mechanical products known as vulcanized fiber whose appli-- cation in the industries is limited by the absence of said property.

Another object of the present invention is to furnish an indurated fiber which, with respect to its mechanical and electrical properties, is comparableto products of this type previously manufactured, but which is water-resistant, and,

therefore, may be employed in the field of electrical insulation under high humidities, a field not open previously to productsof this class.

Still another object of the present invention is to provide processes by which indurated fiber of the desired characteristics may be economically manufactured.

Other objects will be apparent from a consideration of the specification and claims.

Heretofore vulcanized or indurated fiber has been manufactured from various types of cellulose, such as alpha cellulose-or cotton ray paper by treatment of the sheets with suitable hydrolyzing agents such as zinc chloride, aluminum chloride, sulphuric acid, phosphoric acid, mixtures of sulphuric and phosphoric acid, and mixtures of sulphuric acid, phosphoric acid, and

acetic acid, the last named agent being described in Patent No. 1,894,907, dated January 17, 1933. The partially hydrolyzed sheets are superposed one above the other to obtain the desired thickness of the product, and are then subjected to a under heat when wet. Due to these properties,

vulcanized fiber has been largely. manufactured and used in this country. In addition to these properties, indurated fiber manufactured in accordance with Patent No. 1,894,907 has the abilityof flowing or being formed when dry. Attempts have been made to reduce the water-absorption of vulcanimd fiber, but these have not been successful due to the nature of the materials sought to be incorporated in'the vulcanized fiber. Certain of these materials failed to penetrate the.

fibers, while others placed a coating on the fibers, preventing proper gelatinization by'the hydrolyzing agent. The highly water-absorptive character of the vulcanized fiber has prevented its acceptance by the Underwriters Laboratoriesfdue to the fact that its value as a dielectric material is destroyed for all practical purposes under high humidities.

The indurated fiber of the'fpresent inventionis characterized by a} surprising resistance to water and is, therefore; applicable as an insulation material even under highhumidities. The product of the present invention is in addition comparable in all respects with the desirable mechanical andelectrical properties found in the vulcanized fiber products usually manufactured.

The product of the present invention. is an indurated fiber characterized by low water-absorption comprising a plurality of sheets of partially hydrolyzed cellulose joined together and containing a primary aromatic amine-formaldehyde resin, preferablyan infusible, insoluble, thermoplastic aniline-formaldehyde resin within its pores and upon its surfaces associated with said partially hydrolyzed cellulose. The product depending upon its method of manufacture may have the resin homogeneously distributed throughout the sheets of partially hydrolyzed cellulose, or it may have greater amounts of resin at the surfaces of the product than is present in the interior thereof. In fact in some instances, at the center of the product there may be practically no resin associated with the partially.

hydrolyzed cellulose.

The process of the present invention comprises broadly the association of a primary aromatic amine-formaldehyde resin, preferably an infuse ible, insoluble, thermoplastic 'aniline-formalde-- hyde resin with cellulosic material in a process which in general comprises the steps of subjecting cellulosic sheet material to the action of a hydrolyzing agent to hydrolyze the sheets partially, superposing a plurality of said treated sheets one above the other, puring, and drying said superposed material. The association of the resin with the cellulosic material may take place either during or after the fabrication of the sheet material, or before, with, or after the partial hydrolyzing step; as will hereinafter fully appear. The process regardless of the order of the specific steps employed will result in an intimated fiber product characterized by low water-absorption in which the plurality of sheets of partially hydrolyzed cellulose are joined together, and in which a primary aromatic amine-formaldehyde resin is associated with the partially hydrolyzed ing step; Method II by associating the resin with the acid hydrolyzingmgent during the hydrolyzing step; and Method III by the association of the resin with the cellulosic material prior to the 'hydrolyzing step.- as is to be seen from the following charts:

Method 1 Colluloslo shoot mum! Method r1 Cellulosio sheet material Hydrplyling bath Acid bydrolyzing solution conprecipitated resin in 7 solution -Frosted sheets i Buperposlug reeted sheets Pul ing V- r s Resinintbid solution l Resin prccipir ating solution wmmik min Drying Method III Cellulosic pulp Celluloslc m material J, Precipitated resin in chlorhydrln or the like 4 l. .L Besinin acid Suspension of Resin .1: acid such tion precipigated sol: tlon res Resin proclpi- Resin "6m:

tatingnolu on tating solution Pam-making process Hydroly ring bath Superposiugfreated sheets Pur ing such as the usual acids or salt solutions in ,suitable concentrations now utilized in the manufacture of indurated fiber products; for example, zinc chloride, aluminum chloride, sulphuric acid, phosphoric acid or mixtures of sulphuric and phosphoric acid, or mixtures of sulphuric, phosphoric, and acetic acids.

The resins utilizable in conjunctionrwith the present invention are that group of resins which result from the condensation of a primary aromatic amine and a formaldehyde yielding com-- pound in the presence oftan acid. The term primary aromatic amineiqas employed herein includes not only true primary aromatic amines,

such as aniline and its homologues, but also such derivatives thereof which under the conditions of condensation react in the same manner as the primary aromatic amines to yield the same resins, for example, anhydroformaldehyde-aniline, formyl-aniline or the homologues of these compounds. The expression formaldehyde-yielding compound includes not only formaldehyde, but also its polymers and those analogous compounds which under the conditions of condensation split of! formaldehyde andreact in the same manner to yield the same resins. Preferably, the resin employed results from the-condensation of aniline and formaldehyde in the presence of hydrochloric acid as the condensing agent. In place of hydrochloric acid, sulphuric acid, nitric acid, acetic acidand other strong mineral and organic acids capable of forming salts with the primary aromatic amine may be used. The amount of acid employed in the formation of the infusible but thermoplastic resins is usually approximately equivalent molecularly to the primary aromatic amine-so that there is formed in the solution,

' the salt of the amineor the salt of the resin after the reaction of the amine withthe formaldehyde. Acid in excess of this amount is not objectionable. In most cases, it will be desirable to add the acid to the amine prior to the addition of the formaldehyde-yielding compound. Instead of adding the acid separately as the condensing agent, the respective amine salts may beemployed, adding if desired an excess of free acid.

the resin is precipitated. from the solution by the elimination of the effect of the acid which may be accomplished by the addition-of a suitable agent, such as inorganic or organic bases or salts or by extreme dilution which is applicable when an organic acid is used as a condensing agent.

-.An inorganic basic substance, particularly caus- -tic soda, has been found to be especially applicable, although alkaline earth bases, such as calcium hydroxide, may be used with equal facility. The term primary aromatic amine-formaldehyde resin is employed to designate the class of resins" made by reacting a primary aromatic amine and a formaldehyde-yielding compound in an acid solution with the subsequent elimination of 'the effect ofthe acid.

After the condensation in the acid solution.

As has previously been determined, the reaction productsof primary aromatic amines and formaldehyde-yielding compounds obtained in acid solution maybe either fusible or infusible, depending upon the ratio of the formaldehydeyielding compound to the amine. If the ratio of formaldehyde-yielding compound to the amine is or a compound having available aldehyde groups .urea-aldehyde or thiou'rea-aldehyde resins.

the process of the present invention, either the under the conditions of reaction, such as for-'- -m'aldehyde, paraformaldehyde, hexamethylenetetramine, .or any of the potentially reactive aldehyde resins, such as the phenol-aldehyde, In

fusible or the infusible resin may be employed,

but for most purposes a final product is desired in which the resin is infusible. Accordingly, in thepreferred instance, 1 mol. of aniline is reacted in the presence of an equimolecular proportion of acid in solution with more than 1 mol. of formaldehyde. The temperature at which the infusible resins become thermoplastic increases as the formaldehyde content of the resin increases, and, therefore, there is an upper' limit as to the amount of the formaldehyde-yielding compound condensed with the amine which is usually not exceeded, since in the process of the present invention it is advisable to employ a resin which flows at the temperatures used in heating the partially hydrolyzed cellulosic sheets. This temperature obviously must be below that at which damage to the fibers occurs. It has been determined that if a resin is produced by combining 1.05 mols of formaldehyde with 1 mol.-of aniline in the presence of an equimolecular proportion of hydrochloric acid with respect to the amine, the softening point of the infusible thermoplastic resin will be in the neighborhood of 200 F. With 1.15 mols of formaldehyde in the above reaction, the softening point is approximately 250 F.; while with 1.3 mols and 1.4-m0ls of formaldehyde the softening points are approximately 300 F. and 360 F. respectively. From these figures, it will be seen that the formaldehyde content is not usually carried beyond 1,4

to 1.5 mols of formaldehyde to 1 mol. of aniline. When fusible resins are .used in the process of the present invention, it is usually desirable to employthe formaldehyde-yielding compound in a ratio of from .8 mol. to 1 mol. of the compound to 1 mol. of the primary aromatic amine. 'If the fusible resin is employed for impregnation purposes and the infusible but thermoplastic resin is desired in the final product the hydrolyzed cellulosic material containing the resins may be treated with the aldehydic compound, for example, by immersion in a suitable solution, before the final'drying and pressing steps.

As will be seen from the charts, the steps in volving the precipitation of the resin from acid precipitated resin will be used .either in the form I of a suspension'or in solution. While the primary aromatic amine-formaldehyde resins when more a desired to have associated with the sheets.

than one mol. of formaldehyde is reacted with 1 mol. of the primary aromatic amine are-termed insoluble and are in fact insoluble in all the usual organic solvents, they may be dissolvedin certain unusual solvents of the chlorhydrin type, 5

for example," ethylenechlorhydrin, glycolchlorhydrin and glyceroldichlorhydrin. When the solution of the precipitated resin is employed with a chlorhydrin solvent, the solvent is evaporated. after treatment of the cellulosic treatment withthe solution, leaving a resin-impregnated cellulosic material for use in subsequent steps in the process.

Method I When the process of thepresent invention is carried out in accordance with Method I, the cellulosic sheet material is first subjected to the hydrolyzing bath to hydrolyze the cellulosic sheet material partially, and thereafter the sheets are superposed one above the other to obtain the thickness desired in either the form of fiat stock or tubes, as is they usual practice in the manufacture of vulcanized fiber. Preferably the superposed sheets are then pured in order that the hydrolyzing agent may be recovered economically unaccompanied by impurities. The puring step is particularly advantageously carried out at this point if zinc chloride or equivalent salt is used as the hydrolyzing agent, due to the tendency of the resin to become insoluble therein. However, if desired, treatment with the resin in acid solution may immediately follow the step of superposing the partially hydrolyzed sheets,particularly if an acid hydrolyzing agent is employed. The superposed stock is immersed in the acid solution of the resin for a suflicient time to allow the solution to be absorbed by the sheets. This will depend upon the thickness of the superposed stock and the amount of resin. which it is In general, the acid solution will not contain more than 18.5% resin figured as the precipitated resin, since above this percentage difllculties may be encountered in the preparation of the resin solution, or in impregnation. The amount of resin in the solution may vary from this figure downwards, as desired, but usually it will not gobelow since the use of more dilute-solutionsare uneconomical. In the preparation of the acid solution, the aniline is preferably suspended in water and hydrochloric acid is added until a solution which is neutral to Congo paper is obtained. Formaldehyde in solution is then added in the desiredmolecular amounts with respect to the aniline to give the resinfdesired. The solution at the time of the hydrochloric acid is preferably in the vicinity of room temperature, since during the reaction heat is generated, raising the temperature of the solution to some extent, for example, to 60 C. The temperature of the solution may risehigher than this without deleterious results, but sumcient' water is-employed so that the temperature does not approach the boiling point. Thesup'erposed sheets are immersed in the acid solution of the resin until the desired impregnation of the stock by the resin is obtained. yellow coloration'which is found where the solution has impregnated stock. In order to get complete penetration, the 'time of immersion depends upon the thickness of thexstock, for example, in case of approximately 1%; to inch stock, whether the stock be in the form of tubes or flat stock,

the time. of immersion'may be from forty-eight 7 This-maybe determined by the.

hours to seventy-two hours. In a specific case,

tion has been obtained, the stock is immersed in a resin precipitating solution, for example, a solution containing 3% of caustic soda, until the caustic soda has impregnated the stock to the depth previously penetrated by the resin in acid solution and has caused the resin to become precipitated. A visual examination oi'the stock will determine when the resin is precipitated, since the stock containing the precipitated resin is characterized by the whiteness of the precipitate in contradistinction to the yellow coloration of. the resin in acid solution. The time of immersion in the resin precipitating solution varies with the thickness of the stock and the depth .of penetration of the acid solution of the resin.

Usually the immersion in caustic soda is longer than the immersion in the acid solution, due to "the fact that the resin first precipitates near hundred hours in order that the resin may be completely precipitated. At times it may be necessary to treat the stock in the resin precipitating solution for a period of time twice as long or even longer, than the time of immersion in the acid solution of the resin.

After the resin has been precipitated in the stock, it is washedfree from electrolytes and is dried under normal drying conditions employed in the manufacture of vulcanized fiber of the same thickness, the greater the thickness the longer will'be the drying time required. For example, in the case of fi inch stock, the drying usually requires about twenty-four hours at 120 F. to 140 F., while with flinch stock fortyeight hours within this temperature range may be required. After the drying of the stock, it is subjected to such operations as calendering and pressing as may be desired, and thereafter it is' preferably subjected to a heat and pressure treatment sufficient to ,causethe resin to be thermo-.

plastic and to flow around the fibers of the cellulosic sheet material and cloak them.

In the case of sheet stock, after drying, the sheets may be pressed by subjecting them in a hot press, for example, to a temperature of about 340 F. and a pressure of about 100 pounds per square inch for about ten minutes. The stock may then be cooled and calendered which smooths the surfaces and presents them with a suitable finish. In the case of tubes, the dried tubes preferably containing about 3% of moisture may be rolled under pressure with or without heat to consolidate the tubes. This rolling under pressure in the case of tubes presents to them the desired finish. The final heat and pressure treatment may be'brought about in an oven, in an oil bath, or in a press. In the. case of tubes, for example, they may be heated from one-half to four hours, generally in the neighborhood of two hours. at temperatures of 270 F. to.300 F. in anoven or in an oil bath. In the case of sheets, the treatment under pressure is preferred in order to prevent warpage thereof. It will be understood that the factors of temperature, pressure and time may vary widely and are dependent one on the other and upon the thickness of the sheet stock or tube being treated, for example, the pressure used may even be as high as 2100 pounds per square inch. 'It will be obvious that if desired the pressing step may be combined with the final heat treatment step.

The resin content of the finally fabricated sheets depends in general upon the time of immersion of the sheets in the acid solution of the resin for any particular thickness of stock, and may varyfrom a relatively small percentage up to 20% resin content, or even higher. When the water-resistant indurated fiber is made in accordance with Method I, usually a larger resin content is found at the surface of the stock than is encountered in the interior thereof, due to the fact that the rate'of absorption of the resin in acid solution is progressively slowed up as it proceeds inwardly. The resistivity of the product of this method toward water, therefore, depends on the relationship of the thickness to the resin content, that is to say, the thicker the product, the lower the resin content can be. With relatively heavy stock, a resin content of 5.0% will be found to be adequate; while with a very thin stock, it may be desirable to have a resin content of 20% or more.

Tubes \Xater a sorp- I gsgfi tion of Dimensions Type of resin on 3 correspending 24 hours untreated stock Percent Percent Ms inside diameter by lmol. oi aniline to 4. 5 40 M outside diameter. 1.3 mols of formaldehyde. 14 inside diameter by 1 mo]. oi aniline to 10.8 41

5t outside diameter 1.05 mols of formaldehyde 4 142 inside diameter by l mol.oi aniline to 6.5 40

1 outside diameter 1.3 mols of formaldehyde Me inside diameter by 1 mo]. of aniline to 8.8 40

56" outside diameter 1.05 mols of formaldehyde $4" inside diameter by 1 mol. of aniline to 9. 8 41 5% outside diameter 1.05 mols of formaldehyde 91c" inside diameter by lmol. oi aniline to 7.7 40

3e outside diameter 1.05 mols of formaldehyde Sheet stocks Water absorption oi corresponding untreated stock in 24 hrs.

Thiclmess Percent Percent It will thus be seen that the product is resistant to water and that by the process of the present invention a product is provided in which the water absorption is very materially lower than the water absorption of the untreated product.-

In fact, the water absorption encountered in the untreated product renders it unavailable for electrical uses under high humidity. In the product of the present invention, however, the water ab- An acid solution of the resin is prepared by suspending aniline in water and adding hydrochloric acid thereto in amounts sufficient to render the solution neutral to Congo paper. Formaldehyde in solution is then added in sufficient amounts so that the formaldehyde content is equivalent to 1.3 mols of formaldehyde to 1 mol. of aniline. For example, 652 litres of a solution containing aniline hydrochloride in an amount which figured as aniline contains 28.56% thereof is made up to 1,000 litres. Formaldehyde of 38.6% strength is added to the solution in an amount equal to 202 litres. The temperature of the aniline hydrochloride solution made up to 1,000 litres is C., but at the end of the reaction with the formaldehyde, the temperature is increased to 61 C. After the reaction, the solution contains 16.7% resin by weight figured as precipitated resin. Wet pured vulcanized fiber inch in thickness is immersed in the resin solution for seventy-two hours. The fiber is then immersed in a caustic soda solution, preferably of 3% strength, until the caustic soda has precipitated the resin in the pores of the fiber, for example, the time of immersion may be from seventy-two to ninety-six hours. The stock is then washed free from electrolytes and is dried for about twenty-four hours at, 120 F. to 140 F. After drying, the sheets are pressed flat ina hot press for about two minutes at 340 F. and 100 pounds per square inch. The sheets are then cooled and calendered, which smooths the surface giving them the desired finish. The sheets are then subjected to a heat and pressure treatment suflicient to cause the resin to become thermoplastic,

fiir example, ten minutes with a line pressure of v 100 pounds per square inch and a temperature of 325 F. to 340 F.

Example 2 An aqueous acid solution ofthe resin is prepared by, reacting 1 mol. of aniline with 1.05 mols of formaldehyde in the presence of sufficient hydrochloric acid to form aniline hydrochloride.

The dilution is adjusted so that it' contains ap proximately 13.5% of resin by weight. The wet pured gray fiber tubing with an inside diameter of inch and an outside diameter of 5%- inch is immersed in the solution for sixty-four hours.

. The tubes are then removed and placed in a 3% 1 caustic soda solution for one hundred hours. The tubes are then' washed free from soluble salts and dried for forty-eight hours at approximately 120 F. and are then rolled with a moisture content of 3%. The tubes after this process have an inside diameter of 1% inch and an outside diameter of inch. The tubes are then placed in anoven at 290 F," for two hours. After this treatment, a water absorption test in which the tubes are immersed for twenty-four hours in water at room temperature shows that the water absorption is only 7.7%; With tubes similarly treated whose final dimensions are inch inside diameter and inch outside diametenthe water absorption in twenty-four hours is 9.8%.

Method II When the process of the present invention is carried out in accordance with Method I, the cellulosic sheet material to be hydrolyzed partially is immersed in the acid hydrolyzing solution containing the precipitated primary aromatic amine-formaldehyde resin in solution. After the sheets have been partially hydrolyzed in the presence of the resin, the sheets are superposed to obtain the desired thickness and the superposed material either in the form of flat sheet stock or tubes is then pured and thereafter dried. Subsequent to the drying, the superposed sheets are subjected to rolling, calendering or pressing,

While any of the acid hydrolyzing agents may be employed, in this method a hydrolyzing solution containing sulphuric acid, phosphoric acid, and acetic acid such as described in Patent No. 1,894,907, dated January 17, 1933, is preferred. It has been found that this solution is particularly applicable in hydrolyzing cellulosic sheet material and that the primary aromatic amineformaldehyde resin is completely soluble therein. The amount of resin dissolved in the hydrolyzing solution may vary widely, for example, from 2% to 10%, although higher percentages may be utilized if desired. It may be added to the acid hydrolyzing agent as a wet precipitated resin or as a dry pure resin. The dry .pure resin is preferred since the water introduced with the wet resins tends to dilute the acid mixture to a point where the hydrolyzing action is not as efficiently effective. The strength of the hydrolyzing solution and the other factors employed in treating the sheets may be within the ranges described in Patent No. 1,894,907, and, therefore, need not be repeated here.

Example 3 5.2% by weight of dry precipitated resin in the solution. Alpha cellulose paper is then immersed in the solution for a few seconds, The partially hydrolyzed sheets are then superposed one above the other until the desired thickness is obtained and are thereafter pured and dried in the usual manner employed in the manufacture of vulcanized fiber and are subsequently subjected to the heat treatment as disclosed in Method I. The

product upon test shows that it absorbs only 195% water in twenty-four hours. With higher resin contents and proper manipulation, still greater resistance to water can be obtained.

Method m Method III, as has previously been discussed,

contemplates an association of the precipitatedresin with the cellulosic material, making up the' sheets prior to the hydrolyzing step. The resin may be associated with the pulp prior to the manufacture of the paper, or-it may be associated with the finished paper sheets. When the resin is associated with the pulp, it may be added to the pulp in acid solution, for example, in the beater containing partially beaten pulp and may, thereafter be precipitated in and around the fibers by the elimination of the effect of the acid preferably by the addition of a basic solution, or a wet suspension of the precipitated resin may be brought'in contact with the pulp, for example, in the beater. Regardless of the particular method of association the resin with the pulp, it is thereafter manufactured into paper,

for example, by the usual paper-making processes involving the use of l iourdrinier or cylinder machines of the plain or vacuum type. Preferably, the pulp either immediately before or during the paper-making process is washed free from electrolytes.

When it is desired, the cellulosic sheet material after fabrication may be associated with the resin, for example, by passing the paper through the resin in acid solution followed by treatment thereof in a-precipitating solution; or the cellulosic sheet material may be passed through a solution of the precipitated resin in a' solvent of the chlorhydrin type with the subsequent evaporation of the solvent.

The amount of resin associated with the cellulose by either of the two described methods may vary widely and may be relatively low, for example, 5% or may be high, for example, 40%, or more. In general, a resin content of from 5% to. 15% will be found satisfactory. If a high superposed material in the form of tubes or flat sheet stock is subjected to the puring and drying operations as is the case in the manufacture of vulcanized fiber. Subsequently, the superposed material may be subjected to heat treatment with or without pressure to allow the resin to become thermoplastic as, is described in connection with Method'I.

The product ofthe invention when made in accordance with Methods Hand III has the resin homogeneously distributed throughout the sheets in contradistinction to the product made by Method I where usually greater amountsof resin are found at the surface of the product than in the interior thereof. Furthermore, Method 111 permits the tion of larger amounts of resin with the cellulosic material than in either Methods I or II, since the resin is associated with the cellulosic material prior to the hydrolyzing Step. Methodmalsorequlresleastimethan MethodI and is easier to control than Method II and is, therefore, advantageous for use-where the saving of time is an important factor.

sample 4 "470 grams of cotton rag pulp (air dried) are putintoasmallbeatertowhichisaddeddfi cubic centimeters of an acid solution of a resin 'madebyreacting molmfanilinewith 1.9581618 of formaldehyde in the presence of hydrochloric acid.- The resin solution used contains 79 grams of resin figured as the precipitated resin or 15% resin based on the bone dry weight of the pulp. When the resin solution is entirely mixed with the pulp by circulation in the beater, 32 grams of caustic soda dissolved in 1 litre of water are added and mixed thoroughly until the resin is completely precipitated. The stock containing the precipitated resin is removed from the beater, placed on a filter, and washed free of the electrolytes. The washed stock may then be returned to the beater and diluted with water prior to making paper. If desired, the stock may be beaten prior to the addition of the acid'solution of the resin and may also be beaten either before or after the addition of the caustic pre-' cipitating solution. Paper sheets are madeuin any suitable way from the electrolyte-free pulpresin magma, and in commercial production the use of a vacuum typ'e cylinder machine has.

proved to be-particularly applicable. The dried sheets, for example, sheets .009 inch in thickness, are then cut to the desired size. and passed through the hydr'olyzing solution in accordance with the usual practice in the manufacture' of vulcanized fiber, for example, a solution of zinc chloride 71.1 Baum at F. may be used, the

time of immersion being a few minutes. If de-' sired room temperature may be employed, in

.which case a longer time of immersion is required. The sheets are then superposed in the form of sheet stock or tubes and are pured and dried in the well known manner. In the case of tube stock, for example, tubes inch by inch are heated in oil for two hours at C. to C..and then ground to H inch outside diameter. The tubes absorb only 17%% moisture in twentyfour hours in contradistinction to ordinary vulcanized fiber tubes of the same size which absorb 42% moisture in twenty-four hours. In the case of sheet stock, the laminated supe p sed partially hydrolyzed sheets may be treated as described in'Method I. a r Emmple 5 Dry precipitated resin, made by reacting 1 mol. of aniline with 1.3 mole of formaldehyde in the presence of hydrochloric acid with the subsequent precipitation of the resin by the elimination oftheeffect of the acid, is formed 7 into a wet suspension by adding 105 of the resin to a ball mill with 700 cubic centimeters of water; the ball mill being rotated for approximately forty-eighthours. This suspension of precipitated'resin is then added to abeater eontaining 470 grams of pulp (air dried) suspended in water in accordance with the usual papermaking practice. After a thorough mixing is obtained by circulation inthe beater, paper sheets are made from the pulp-resin magma which are thereafter dried, treated with a hydrolyzing agent, superposed, pured, and dried in accordance withwell known methods employed in making-vulcanized fiber as hereinb'efore de scribed in connection with other examples. If desired, the sheet or tube stock thus formed may be subjected to the heat treatment step herein-.

before described. The product is comparable in properties and water resistivity to the products made by the other methods herein set forth.

l mntple 6 An absorbent paper sheet, for example.

cotton paper, is passed slowly throughanacid specific figures being merely illustrative.-

solution of a resin, which solutions contains, for

example, 8% of any desired aniline-formaldehyde resin, the paper becoming saturated with the resin solution. The excess solution may be removed from the paper sheets by passing them through squeeze rolls or otherwise and the sheets are subsequently passed slowly through a 3% solution of caustic soda in order to precipitate, the resin, the time of immersionin the caustic solution being about two minutes. After this treatment, the electrolytes are removed by washing in water and the sheets dried. The dried paper sheets of any desired size are then treatedwith a hydrolyzing solution, superposed, pured; and dried by the .usual methods of manufacturing vulcanized fiber. Thereafter, if desired, the product may be heat treated as described herein. The product, like the products of other processes, is characterized by high water-resistivity.

Example 7 88.5 grams of wet pure resin, containing 89.6% water, made by reacting 1 mol. of aniline with 1.3 mols of formaldehyde in the presence of hydrochlo-ric' acid with the subsequent precipitation of the resin by the elimination of the effect of the acid, is added to 219 grams of ethylenechlorhy drin. The resin for the most part dissolves in the ethylenechlorhydrin, but the very small fraction which remains insoluble is removed by filtration. The filtered solution contains 2.7% resin by weight. Sheets of unsized absorbent cotton paper are passed through the clear solution until the sheets have become impregnated therewith. If necessary or desirable, the sheets may be dried and subsequently immersed again in the solution of the resin. The resin impregnated strips after the final drying are treated with a hydrolyzing agent, superposed, pured and dried by the well known methods of making vulcanized fiber. The sheet or tube stock thus made may then be treated by the heat and pressure steps herein described, for example, they may be heated for one hour under dry heat at 105 C. followed by treatment for one and one-half hours under dry heat at 152 C. The product obtained differs markedly from vulcanized fiber, since it has a very low water-absorptive capacity.

From the above description, it is to be noted that the present invention contemplates a process in which the sheets are placed in superposed'relation while still moist. This results in a binding of the sheets together by the hydrolyzed cellulose although when the superposed material is subjected to the final heat treatment the resin may also aid in the binding of the individual sheets together. In the product of the present invention, however, the hydrolyzed cellulose is relied upon at. least ,in part to bind the superposed sheets. No claim is laid herein to the invention of drying the partially hydrolyzed sheets associated with the resin prior to the step of superposing, the same being the subject matter of a co-pending application filed by Gustave Widmer on May 12,

1933, Serial No. 670,795.

While in the foregoing examples resins made by combining given percentages of the primary aromatic amine and the formaldehyde have been recited, it will be clear from the specification that any desired primary aromatic amine-formaldehyde resin, whether fusible or infusible, may be employed. Also the times, temperatures, pressure and other conditions mentioned may vary widely within the skill of a the operator, the

Considerable modification is possible in the choice of the cellulosic material, the hydrolyzing agent, and the primary aromatic amine-formaldehyde resin employed, as well as in the steps of the process and the physical factors employed in carrying out the process without departing from the present invention.

I claim:

1. An indurated fiber product characterized by low water absorption, comprising a plurality of superposed sheets of partially hydrolyzed cellulose joined together and containing a primary aromatic amine-formaldehyde resin within its.

present in greater amounts at the surfaces of the product than at the interior thereof.

5. The product of claim 4 wherein the resin is an aniline-formaldehyde resin.

6. The product of claim 4 wherein the resin is aninfusible, insoluble, thermoplastic anilineformaldehyde resin.

7. An indurated fiber product characterized by low water absorption, comprising a plurality of superposed sheets of partially hydrolyzed cellulose joined together and containing a primary aromatic amine-formaldehyde resin .associated with said partially hydrolyzed cellulose and homogeneously distributed through the said product.

8. The product of claim 7 wherein the resin is an aniline-formaldehyde resin.

9. The product of claim '7 wherein the resin is an insoluble, infusible, thermoplastic anilineformaldehyde resin.

10. In the process of making an indurated fiber product of low water absorption by subjecting hydrolyzable cellulosic sheets to the action of a. cellulose hydrolyzing agent to hydrolyze the sheets partially, superposing a plurality of said sheets one upon the other to cause adherence of said sheets by the partially hydrolyzed cellulose, washing and drying said superposed material, the step which comprises associating a primary aromatic amine-formaldehyde resin which, has been precipitated from the acid salt of said resin by the elimination of the acid therefrom, within the pores and upon the surfaces of the cellulose material of said sheets in a stage in said process prior to the drying of said superposed material. v

washing the product, and thereafter drying it.

employed is an iniusible, insoluble, thermoplastic 14. The process-o1 claim 13 in which the resin employed is an aniline-formaldehyde resin.

15. The process oi claim 13 in which the resin employed is an infusible, insoluble, thermoplastic aniline-formaldehyde resin. 1 i

16. The process of making an indurated-flber product of low water absorption which comprises immersing hydrolyzable cellulosic sheet material in a hydrolyzing solution to hydrolyze said sheets partially, superposing said sheets one above the other, to obtain the thickness desired and to cause adherence of said sheets by the partially hydrolyzed cellulose, puring said product, immersing said superposed product in an acid solution oi. a primary aromatic amine-formaldehyde resin until the solution has penetrated said product, immersing said product in a-resin precipitating solution until said resin has precipitated within the pores of the product, washing and drying the product, and thereafter subjecting it to heat treatment to cause the resin to flow around the fibers. i

17. The process of claim 16in which the resin is an aniline-formaldehyde resin.

18. The process of claim 16 in which the resin employed is an iniusible, insoluble, thermoplastic aniline-formaldehyde resin.

19. The process of making an indurated fiber product of low water'absorption which comprises immersing cellulosic sheet material in an acid hydrolyzing solution containing in solution a primary aromatic amine-formaldehyde resin, said resin having been precipitated from acid solution, superposing said resin-impregnated par-.. tially hydrolyzed sheets one above the other, puring and drying said superposed material.

20. The process of claim 19 in which the resin is an aniline-formaldehyde resin.- I

21. The process 01 claim 19 in which the resin aniline-formaldehyde resin.

22. The process of making an indurated fiber product of low water absorption which comprises immersing'cellulosic sheet material containing a primary aromatic amine-formaldehyde resin, said resin having been precipitated from acid solution by the elimination oi! the acid therefrom, in a hydrolyzing solution' to partially hydrolyze said cellulose, superposing said sheets one above the other puring and drying said product.

23." rne process 01' claim 22 in which the resin is an aniline-formaldehyde resin.

24. The process of claim 22 in which the resin employed is an intusible, insoluble, thermoplastic aniline-tormaldehyde resin.

25. The process of making an indurated fiber product of low water absorption which comprises immersing cellulosic sheet material in an acid solution 01' a primary aromatic amine-formaldehyde resin until said sheets have become impregnated bysaid resin, immersing said resin-containing sheet material "in a resin precipitating solution to cause precipitation of the resin, imm'ersing said resin-containing paper in a hydrolyzing solution, superposing said sheets one above the other, puring and' drying said product.

, 26. The process of claim 25 in which the resin is an aniline-formaldehyde resin.

27. The process or claim 25 in which the resin employed is an iniusible, insoluble, thermoplastic. aniline-formaldehyde resin.

28.- The process of making waterproot indurated fiber oi. low water absorption-which com-- prises immersing cellulosic sheet material in a chlorhydrin solution 01' a primary aromatic amine-formaldehyde resin, said resin having been precipitated from acid solution by the elimination or the acid therefrom, causing said sheet material to become impregnated by said resin, immersing said resin-containing paper in a hydrolyzing'solution, superposing said sheets one above the other, puring and drying said product.

29. The process of claim 28 in which the resin 

